The optimum operation of a suction operated automatic swimming pool cleaner is usually very much dependant on the rate of flow of water through the cleaner. Too much flow tends to make the cleaner adhere too tightly to the surface being cleaned and too little flow prevents propulsion of the cleaner.
Several kinds of valve have been developed for this specific use and do operate with a greater or lesser degree of success. Some tend to choke on debris in the pool water, others are relatively complicated constructions and some by nature of their location in the pool filtration system induce vortex flow and the admission of air into the filtration system.